Haemoglobin

Question 1

Haemoglobin binds to oxygen cooperatively. What does this mean?

Answer 1

It means that when oxygen binds to a site on one chain it increases the likelihood

Question 2

What is the prosthetic group in haemoglobin and myoglobin?

Answer 2

Haem

Question 3

What are the components of haem?

Answer 3

Haem is comprised of the organic compound protoporphyrin and a central iron atom.

Protoporphyrin is made up of four pyrrole rings, four methyl groups, two vinyl groups, and two propionate side chains are attached.

Question 4

What is the chemical name for haem?

Answer 4

Fe-protoporphyrin IX

Question 5

The iron atom lies in the center of the protoporphyrin, bonded to the four pyrrole ________ atoms. Although the haem-bound iron can be in either the ferrous (Fe^__) or ferric (Fe^__) oxidation state, only the Fe^__ state is capable of binding oxygen.

Answer 5

The iron atom lies in the center of the protoporphyrin, bonded to the four pyrrole nitrogen atoms. Although the haem-bound iron can be in either the ferrous (Fe2+) or ferric (Fe3+) oxidation state, only the Fe2+ state is capable of binding oxygen.

Question 6

The iron ion can form two additional bonds, one on either side of the haem plane. These bonding sites are called the _____ and _____ coordination sites. In myoglobin, the _____ coordination site is occupied by the imidaxole ring of a histidine residue from the protein. This histidine is referred to as the ________ histidine.

Answer 6

The iron ion can form two additional bonds, one on either side of the haem plane. These bonding sites are called the fifth and sixth coordination sites. In myoglobin, the fifth coordination site is occupied by the imidaxole ring of a histidine residue from the protein. This histidine is referred to as the proximal ​histidine.

Question 7

How does oxygen bind to haem? What are the changes that occur upon binding?

Answer 7

Oxygen binds to the sixth coordination site on haem.

The binding of oxygen at the sixth coordination site rearranges the electrons within the iron ion so that it becomes smaller, allowing it to fit into the porphyrin ring and lie inside the porphrin plane.

Question 8

How does the structure of haemoglobin prevent the release of reactive oxygen species?